Field of the Invention
The present invention relates generally to method and apparatus for joining tubular materials to one another and to a method and apparatus for joining members formed of dissimilar materials to one another.
Description of the Related Art
Tubes are used in a variety of fields and for a variety of purposes. For instance, tubular members are used in the medical field in medical devices. One application of tubular members is as a component of a system for delivery of medical devices to locations within the human body such as within any lumen of the body. For example, the tubes may be used to deliver medical devices within the vasculature, the biliary system, the esophagus or the gastro-intestinal tract. Of course, tubes are used in many other fields and for many other purposes as well.
It is sometimes necessary to join two tubes to one another and in some applications it is important that the joining of the tubes not result in an increase in the outside diameter of the tubes at the joint and that the joining not result in a decrease in the inside diameter of the tubes at the joint. Where tubes to be joined are of a similar material, it may be possible to join the tubes by welding using a so-called butt joint. Where dissimilar materials are to be joined, the materials may not be readily weldable to one another. Some tube materials may be joined by gluing, brazing or soldering of the butt joint; however, it may be problematic to join dissimilar materials even with these techniques and the fact that only a small bonding surface area is available at the joint can result in a joint that is not sufficiently strong.
A lap joint increases the joint strength by increasing the bonding surface area but increases the wall thickness at the joint. A half lap joint where the material thickness of both parts is reduced in the joint area, resulting in a larger bonding area with no increase in the wall thickness at the joint, may not be practical for thin wall tubes. Lap joints between dissimilar tubular materials can be weak or require substantial overlap areas to achieve adequate bond strengths.
Other techniques for joining tubes to one another are possible, such as press fit, shrink fit, crimping, or the like, but these result in either an increased outer diameter, a decreased inner diameter, or both. Other joining techniques may also result in deformation of the tube, weakening of the tube, or other issues.
Joining dissimilar materials in general can also be troublesome, such as when it is necessary to join a tube to another member such as a tube or a cable, particularly where the tube and other member are of different materials. For instance, welding of nitinol to stainless steel results in brittle intermetallic compounds, such as TiFe and TiFe2, which makes the resulting weld brittle. Using an intermediate material to avoid the formation of such brittle compounds is not practical in all applications.
Thus, joining tubes of dissimilar materials can be problematic if the materials are not readily weldable to each other nor reliably joined by other means such as brazing, soldering, gluing, press fit or shrink fit. This is particularly true where it is desired to create a joint connecting tubes or other members without an increase to the outside dimensions of the tube and without decreasing the inside dimensions of the tube.